There are several formats currently available for encoding motion pictures, i.e., a temporal sequence of images. Some of these formats are standards and include, but are not limited to, the standards commonly known as MPEG-2 (formally known as ISO/IEC 138182 or ITU-T Rec. H.262) and H.264 (formally known as ISO/IEC 14496-10 or ITU-T Rec. H.264). Other formats may borrow concepts from or use parts of these standards. For example, a format known as HDV encodes a progressively scanned high-definition image sequence captured at a rate of 23.976 frames per second using MPEG-2 encoding. The captured image sequence is encoded as an image sequence at a second image rate, e.g., 29.97 frames per second or 59.94 fields per second, with information in the encoded image sequence indicative of fields or frames that are repeated when decoded. In MPEG-2, this information includes a value known as a “repeat first field flag.” In H.264 this information is provided by a variable called “pic_struct.”
It can be difficult to edit a video program using an image sequence that has been encoded using repeated fields or frames. In particular, it is difficult to maintain accurate timing relationships between sources of image sequences and the edited video program. Such timing requires a proper understanding and use of the information that indicates whether a field or frame is repeated in a wide variety of possible editing operations.